In recent years, storage capacity of a hard disk and the like in a computer apparatus has increased, which has increased the density of information recording on a single recording surface. For example, in order to increase the recording capacity in a magnetic disk, the surface recording density needs to be increased. However, as the recording density increases, the recording area occupied by one bit on the recording medium decreases. When this bit size is reduced, the potential energy of the state in which one bit information is recorded becomes close to the thermal energy at room temperature, which may cause a thermal demagnetization problem in which, for example, recorded information is inverted or lost due to thermal fluctuation or the like.
An in-plane recording method that has been widely used is to record magnetism such that the direction of magnetization is parallel to the surface of the recording medium. However, this method may easily cause the loss of recorded information or the like due to the above-described thermal demagnetization. Thus, in order to resolve this problem, the recording method is shifting toward a perpendicular recording method to record magnetization signal in the direction perpendicular to the surface of the recording medium. This method is to record magnetic information by moving a magnetic monopole closer to the recording medium. This method causes the recording magnetic field to be almost perpendicular to a recording film. Information recorded with a perpendicular magnetic field tends to keep stable in energy, because it is difficult for the north pole and the south pole to form a loop on the surface of the recording film. In this regard, the perpendicular recording method is more resistant to thermal demagnetization than the in-plane recording method.
However, for a modern recording medium, further increase in density is needed to meet a demand for recording/reproducing even larger amount and higher density of information. To this end, in order to minimize the influence between adjacent magnetic domains and the thermal fluctuation, high-coercivity materials are beginning to be used as a recording medium. This makes it difficult to record information to the recording medium even if the above-described perpendicular recording method is used.
Thus, in order to resolve this problem, a hybrid magnetic recording method (near-field light assisted magnetic recording method) is suggested, which is to locally heat a magnetic domain with near field light to temporarily reduce the coercivity and perform writing while the coercivity is reduced. The hybrid magnetic recording method uses near-field light generated by the interaction between a very small area and an optical aperture of a size equal to or less than the wavelength of light, formed on a near-field optical head. In this manner, using a very small optical aperture exceeding the diffraction limit of light, that is, a near-field optical head having a near-field light generating element, it is possible to heat one of the areas the size of each of which is equal to or smaller than the wavelength of light, which is the limit for conventional optical systems. This can provide recording bits with higher density than that can be provided by conventional optical information recording/reproducing devices.
Note that the near-field light generating element is not limited to the one with the very small optical aperture as described above, but may also be one with a protruding portion formed in nanometer size, for example. This protruding portion can also generate near-field light as the very small optical aperture can.
Various recording heads using the hybrid magnetic recording method described above are provided. One of them that is known is a magnetic recording head that reduces the size of light spot to increase the recording density (see JP-A-2004-158067 and JP-A-2005-4901, for example).
This magnetic recording head generally includes: a main magnetic pole; an auxiliary magnetic pole; a coil winding in which a conductive pattern is provided in a spiral shape in the same plane, the main magnetic pole passing along the central axis of the spiral shape, the conductive pattern being formed within an insulating material; a metal scatterer for generating near-field light from radiated laser light; a planar laser light source for radiating laser light toward the metal scatterer; and a lens for focusing the radiated laser light. These components are mounted on the tip surface of a slider fixed to the tip of a beam.
One end of the main magnetic pole is a surface facing a recording medium, while the other end is connected to the auxiliary magnetic pole. In other words, the main magnetic pole and the auxiliary magnetic pole form a magnetic-monopole-type perpendicular head that is one magnetic pole (magnetic monopole) disposed in a perpendicular direction. Also, the coil winding is fixed to the auxiliary magnetic pole with a portion of the coil winding passing through between the main magnetic pole and the auxiliary magnetic pole. The main magnetic pole, the auxiliary magnetic pole, and the coil winding form an electromagnet as a whole.
The metal scatterer including gold and the like is mounted on the tip of the main magnetic pole. The planar laser light source is disposed spaced from the metal scatterer. The lens is disposed between the planar laser light source and the metal scatterer.
For the above-described components, the auxiliary magnetic pole, the coil winding, the main magnetic pole, the metal scatterer, the lens, and the planar laser light source are mounted in this order from the tip surface of the slider.
The magnetic recording head configured in this way records various information to the recording medium by applying recording magnetic field while generating near-field light.
Specifically, the planar laser light source radiates laser light. This laser light is focused by the lens and then applied to the metal scatterer. Then free electrons within the metal scatterer are caused to uniformly vibrate by the electric field of the laser light, which excites plasmons to generate near-field light at the tip portion of the metal scatterer. Consequently, a magnetic recording layer of the recording medium is locally heated by the near-field light, with its coercivity temporarily reduced.
Also, by supplying drive current to the conductive pattern of the coil winding while radiating the laser light, the recording magnetic field is locally applied to the magnetic recording layer of the recording medium near the main magnetic pole. This allows various information to be recorded to the magnetic recording layer with its coercivity temporarily reduced. Thus, recording to the recording medium can be performed by the cooperation of the near-field light and the magnetic field.
Another known magnetic recording head includes an additional preheating mechanism combined with the above-described magnetic recording head (see JP-A-2005-78689, for example).
This magnetic recording head includes a resistance heater as the preheating mechanism between the above-described main magnetic pole and auxiliary magnetic pole. The area of the tip of this resistance heater is larger than that of the main magnetic pole and the auxiliary magnetic pole, and accordingly, the resistance heater can heat a large area and has a low temperature gradient. So, the resistance heater is configured to be able to apply heat that is only a preheating level to the magnetic recording layer of the recording medium.
The magnetic recording head configured in this way can preheat the magnetic recording layer in advance with the resistance heater, which can reduce the heat generation at the metal scatterer generating the near-field light. As a result, the degradation, possibility of damage and the like of the metal scatterer due to an increased temperature can be reduced to improve the endurance.
Patent Document 1: JP-A-2004-158067
Patent Document 2: JP-A-2005-4901
Patent Document 3: JP-A-2005-78689